DIETARY STARCH DILUTION STRATEGIES TO IMPROVE RUMEN HEALTH AND PERFORMANCE IN FEEDLOT CATTLE
ABSTRACT The objectives of this study were to evaluate the effects of starch dilution with different sources of dietary fiber from terminal implant to slaughter on feedlot cattle performance, carcass characteristics, and rumen buffering characteristics. Steers (n = 416; 372 ± 2.67 kg) were allocated to 48 pens in a randomized complete block design. Pens of cattle (n = 12 per treatment) were assigned to 1 of 4 treatments consisting of steam-flaked corn-based diets containing: 1) CON; 7.50 % corn stalks on a DM basis fed for the entire feeding period, 2) CS; 14.75% corn stalks on a DM basis fed from terminal implant to slaughter, 3) WD; 9.50% wet distillers grains with solubles, and 7.50% corn stalks on a DM basis fed from terminal implant to slaughter, and 4) NR; 19.00% wet distillers grains with solubles, and 0.0% corn stalks on a DM basis fed from terminal implant to slaughter. Six days before administration of the terminal implant, steers were transitioned to their treatment diets using a two-ration system, whereas CON consumed the same diet throughout the entire feeding period. Within each pen, 2 steers were randomly selected to receive an indwelling ruminal pH bolus to quantify rumen pH and a 3-axis accelerometer tag to assess rumination time. Diet samples were collected weekly to determine particle size, NDF concentration, and physically effective fiber (peNDF). At slaughter, rumens were evaluated for the presence of scarring and lesions. Performance (BW, DMI, ADG, G:F) was not different (P ≥ 0.34) from initial to transition. Dry matter intake and metabolizable energy intake from transition to final were greatest for cattle consuming CS, intermediate for WD and CON, and least for NR (P < 0.01). Final BW and ADG did iv not differ among treatments from transition to final (P ≥ 0.19); however, G:F was greatest for NR, intermediate for WD, and least for CS and CON (P = 0.10). There was no difference (P ≥ 0.24) in hot carcass weight, dressing percentage, marbling score, quality grade, yield grade, and percentage KPH fat among treatments. Steers consuming CS had greater (P = 0.08) 12th rib fat thickness. The proportion of abscessed livers did not differ (P = 0.26) among treatments. The peNDF was greatest for CS, intermediate for WD and CON, and least for NR (P < 0.01). Particles > 4.0 mm were greatest for CON and CS, intermediate for WD, and least for NR (P < 0.01). A treatment × day interaction (P < 0.01) was observed for daily rumination minutes and rumination per kg of DMI; rumination was greater for CS, intermediate for WD and CON, and least for NR early in the finishing period and greater for CS than NR towards the end of the finishing period. Similarly, a treatment × hour effect (P < 0.01) was observed for hourly rumination; cattle consuming CS had greater rumination than NR at 0200, 0400, 0600, 1200, 1400, 2000, 2200 and 2400 h. There was also a treatment × day interaction (P < 0.01) for rumen pH, but the diet appeared to have minimal effects on pH throughout the entire feeding period. A treatment × hour effect (P < 0.01) was observed for hourly pH; cattle consuming CON had greater rumen pH than WD and NR at 0400, 0600, and 800 h, but had minimal effects throughout the remainder of the 24 h period. Rumen scores of cattle consuming CON had a greater (P = 0.09) percentage of rumen score 3, but there were no other differences among dietary treatments (P > 0.31)The results of this study indicate that increasing the proportion of corn stalks in the diet post-terminal implant administration increases DMI, dietary peNDF, and rumination time. However, ruminal pH was v minimally impacted by decreased starch and greater fiber provided from either corn stalks or WDGS and suggests that roughage can be replaced with fibrous corn milling byproducts without negatively impacting rumen health.